Modulating method and apparatus



April 14, 1925. 1,533,157

- w. E. BEATTY MODULATING METHOD AND APPARATUS Filed Dec. 11, 1919 //1 van far:

VVf/fiam Bea/7y by Wm/y I a citizen of theUnited States,

- of a modulator of the -qency waves or impulses.

' provide a system Patented Apr. 14, 1925 UNITED STATES PATENT OFFICE.

WILLIAM E. BEATTY, OF BAYS IDE,'NEW YORK, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, 0']? NEW YORK, N. Y., A CORPORATION OF NEW YORK.

monona'rme METHOD AND APPARATUS.

Application filed December 11, 1919. Serial No. 344,039.

To aZZ whom it may concern:

Be it known that I, WILLIAM E. BEA'rrY, residing at Bayside, in the county of Queens and State of New York, have invented certain new and useful Improvements in Modulating Methods and A paratus, of which the following is a full, 0 earrconcis'e, and exact description.

This invention relates to modulating methods and apparatus, and more particularly to methods and systems for modulating alternating currents by means of electron-discharge devices in which the electron= emitting power of the cathode is Varied 1n accordance with signals or other low fre- An object of the invention is to provide a method for variably controlling the transmission of energy in accordance with the characteristics of a given energy wave.

Another object of the invention is to control the value of an alternating or other fluctuating electrical current by varying the ionic activity of a member which the current tolbe controlled is caused to traverse.

Another object of the invention is to provide a modulating device in which the electron emitting power of a cathode element may serve to vary the value of the discharge current passing through the device.

A feature of the invention is the provision electron discharge type having normallyno discharge current.

A further feature of the inventionis a combined oscillator and modulator in which the amplitude of the oscillations produced may be varied according to the thermionic condition of a cathode.

An additional object of the invention is to ,for transmitting pure modulated waves. 7 1

According to this invention carrier oscillations to be modified or modulated are supplied to a circuit connected to the cathode anode of an electron discharge device, or

device may be arranged, as is now wellthat the heating power of the cathode as, for example, by varying its temperature and so to correspondingly vary the amplitude of the resulting oscillations in the external cathodeanode circuit. If a low frequency control or signal current circuit is so related to the cathode as current to vary the electron emissivity of the cathode in accordance with the low frequency signal or control current, and a transmission circuit is suitably associated with the external cathode-anode circuit, carrier oscillations'varying in amplitude in accordance with the low frequency current may be supplied to the transmission circuit.

In the drawing, Fig. 1 illustrates a radio signaling system embodying a two-element electron discharge device opera-ting in accordance with this invention as a modulator. Fig. 2 illustrates a modification of the system shown in Fig. 1 in which the cathode of the thermionic discharge device is normally without heating current. Fig. 3 illustrates a modification employing a double tube modulating device in an absorption system, and Fig. 4 a modified radio system making use of a combined oscillator and modulator.

Referring to Fig. 1, carrier oscillation source 1 is shown coupled by transformer 2 to a circuit 3 which includes the two-element electron discharge device 4 and primary winding of transformer 5 by means of which circuit 3 is coupled to an antenna or transmission c rcuit 6. The thermionic discharge device inc'udes a hot filamentary cathode 7 and a plate or anode 8. Cathode 7 is-heated .to a definite temperature by current from source 9 in circuit there; 0

a direct current with. A microphone 10 in series with a talking current source 11 and primary winding of a transformer 12 serves to impress upon the heating circuit of the cathode an additional current varying in accordance with signals.

In Fig. 2 the circuit arrangements are the same as in Fig. 1 with the exception circuit of the filamentary cathode includes no direct current source and that the oscillation source 1 'is introduced directly into circuit 3. A closed loop circuit 13 is interposed in the cathode-heating circuit and is tuned to the frequency of carrieroscillation source 1.

to cause the low frequency Referring to Fig. 3, carrier oscillationsource 14 is shown coupled to antenna or transmission circuit 15 by a transformer 16- having three sets of windings. An electric discharge device 17 having a hot filament or other cathode 18 and two plate'electrodes is connected to antenna 15 by one set of the windings of the transformer 16 in such mannor than an electromotive force induced in one of these windings from the carrier current source tends to make the corresponding plate electrode or anode positive with respect to the filament and at the same time to make the other anode negative with respect to the filament. The filamentary cathode is supplied with heating currentby a transformer 19 connected to the signaling or control circuit 20 by an amplifying device 21, preferably of the thermionic type.

In Fig. 4, a three-element electron discharge device comprising a hot cathode 22, an anode 23, and an impedance control element or grid 24 has its input and output circuits so connected as to cause said device to act as an oscillator of wellknown type. The cathode is heated by amplified signal or control currents in the same manner as in the :ystem illustrated in Fig. 3, and the heatin current circuit includes a tuned loop circult 25 similar to circuit 13. A condenser 26 and inductances 27, which are preferably but not necessarily coupled to each other, constitute, with the primary winding of transformer 28, an oscillatory circuit which substantially determines the frequency of the oscillations generated. A source 29. serves to supply space. current to the discharge device.

In the arrangement of Fig. 1 the filamentary cathode is heated to such a point that the electron emission will rapidly change as its temperature is increased. The cathodes employed in the discharge devices of this invention are preferably filaments specially designed to have high resistance, hence requiring small heating currents, and are preferably of small cross section in order to permit rapid heating and cooling. Preferably the temperature of the filament in Fig. 1 is normall such that for all lower temperatures su stantially no electron emission ooours, while for higher temperatures the emission varies according to the energy sup-' plied. Preferably, also, the high frequency electromotive force applied to the discharge circuit 3 is sufiiciently large to saturate the tube or discharge device for the entire range of temperature operation of cathode 7. If this is the case the amplitude of the transmitted oscillations will vary directly as the electron emission power ofthe cathode. Consequently, as the electromotive force applied to the heatin circuit from the signal circuit is varied, t e electronic activity of the device is correspondingly varied and the yalueflof the high frequency energy trans"- mitted by the tube is accordingly changed. The carrier oscillations transmitted to the antenna 6 and radiated thereby will accordingly be of the nature of a modulated wave.

In the system of Fig. 2, the circuit 13 prevents current of the high frequency supplied by source 1 from traversing the heating circuit vof the cathode and being impressed upon the low frequency signaling circuit. During non-signaling periods the cathode of this modification is not heated and, inasmuch as any flow of high frequency energy in circuit 3 depends upon the activity of the electron discharge device, no high frequency energy is transmitted at such time's. This cathode is preferably of a type which will not require initial heating to bring it to electron emitting condition and the electron emissivity of which will vary in accordance with the energy'of the low frequency curnent supplied. ll his modificae tion, like that of Fig. 1,'accordingly serves to transmit modulated waves.

In the modification of Fig. 3, source 14 serves to supply high frequency currents to the antenna 15 and tube 17 coupled to the antenna serves asv an absorbing device to variably divert energy from the antenna. The amount of energy diverted depends upon the temperature of cathode 18 of discharge device 17 and this temperature varies in accordance with the value of the signal currents in circuit 20. Inasmuch as device 17 has two asymmetrically conducting paths reversely connected to the antenna, it acts to absorb energy during both half cycies of the high frequency current. Amplilie? 21 serves to increase the variations in the filament temperature and so to make the electron emissivity of the cathode 18 to vary in accordance with the amplitude of low frequency signal waves in circuit 20. The unabsorbed energy of antenna 15 is, therefore,

transmitted as a wave varying in amplitude with the low frequency signal or control currents.

In the system of Fig. 4, the electron discharge device operates in conjunction with the oscillatory circuit 26, 27 to produce oscil lations of a frequency determine-d chiefly by the electrical constants of the oscillatory circuit, and of an amplitude which is a function of the space current of the discharge device. This space current depends directly upon the number of available electrons emitted from the cathode, and hence upon the value of the variable current supplied by low frequency signaling circuit 20. Modulated oscillations will, therefore, be supplied to the antenna, the discharge device serving both as an oscillator and as a modulator. During non-signaling periods, the cathode is thermionically inactive and no oscillations are produced.

For telegraphic or control energy trans- Im'ssiomthe microphone circuit may be replaced by a key controlled buzzer circuit. In lieu of the antenna shown for radio transmission, conducting lines may be substituted for transmission by electric currents.

Although the invention has been described in connection with certain specific radio signaling systems, it is applicable to teledynamic operation generally, Whether, by radio or Wire transmission. In certain aspects the invention is not limited to transmission but relates broadly to the control of varying current. The invention is, therefore, not to be limited by the specific disclosure but only by the scope of the appended claims.

What is claimed. is:

1. The method of variably controlling a current in accordance with signal Waves which comprises causing said current to pass as an electron discharge from a cathode normally electronically inactive and simultaneously maintaining the electron emis-. sivity of said cathode substantially proportional to the amplitude of said signal Wave.

2. The method of transmission which comprises causing periodic energy to pass as an electron discharge from a cathode normally electronically inactive and constantly maintaining the electron emissivity high frequency electromotive force between an anode and a Cfl. l3l1OCl8-Wl1l0h is normally electronically inactive and causing said cathode to become electron emitting substantially direct proportion to the ampli tide of a low frequency modulated Wave.

5. An electron discharge device comprising a cathode normally electronically inactive, an anode and means for varying the electronic activity of said cathode substantially directly in proportion to a given signal current.

6. An electron discharge device comprising a cathode normally electronically inactive, an anode, means for impressing a pcriodic electromotive force between said cathode'and said anode to produce an electron discharge therebetween, and meansfor varying the electronic activity of said cathode substantially in accordance with the amplitude of a low frequency Wave.

7. An electron discharge device comprising a cathode normally electronically inactive, an anode, means for varying the electronic activity of said cathodein accordance with the amplitude of a given low frequency Wave, and means for impressing between said cathode and said anode a periodic electromotive force of intensity sufiicient to saturate said discharge device throughout the range of the electronic activity of said cathode.

8. An electric discharge device comprising a cathode and an anode, means for setting up. an electro-motive force between said cathode and said anode, said cathode being normally electronically inactive, and means for causing said cathode to become electronically active in accordance with low frequency currents.

9. A modulator comprising an electric discharge device having a cathode and an anode, means for setting up an alternatin electromotive force between said cathode and said anode, said cathode normally emitting substantially no electrons, and means controlled by signals for rendering said cathode electron emitting.

In witness whereof, I hereunto subscribe my name this 8th day of December A. D.,

WILLIAM E. BEATTY. 

